This is an idea I'm gauging the interest on. I already have a script that allows the automated delivery of ebooks when people make a sale / win an aution (http://www.digi-download.co.uk) and I have another script that sets up an autoresponder which is triggered on a variable time scale (http://www.sticky-scripts.com)

My idea is to amend the autobot to work via PayPal subscription service, ie once people have paid their monthly dues, they are sent details of where to download their ebook / software from.

This could then be used for sites that run courses, with a different lesson being sent each month. It could be a "Book of the Month" type thing and so on.